一个条形橡皮擦放在水平桌面上，下列说法：
①它的硬度大于铁的硬度；    ②它的导热性比铜的导热性差；
③使用后，其密度保持不变；  ④若把它放在水中，一定浮在水面上；
⑤无论怎样放置，它对桌面的压强都相同。合理的是(    )

增加：在缺词处加一个漏字符号（ ）,并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1). 每处错误及其修改均仅限一词；

2). 只允许修改10处，多者（从第11处起）不计分。

    When I was a child, I spent more than ten years learn the violin．Therefore, I couldn't understand "real music"．After I graduated at high school, a friend of mine suggested that we started to learn the guitar because we all thought it was cool．l will never forget the day on that we went to buy guitars in the guitar store．There I saw a guitar player playing the guitar, which I really enjoyed．He became my the first guitar teacher．It took me such a long time choose a guitar among several wonderful model．Now the guitar is the most importantly part of my life and I practise it every day.

如果水位升高3m时水位变化记作+3m，那么水位下降5m时水位变化记作（　　）

根据首字母提示，用适当的词填空，每空一词。